function func(str) {
	var promise = new Promise(resolved => {
		setTimeout(() => {
			resolved(str);
		}, 10);
	});
	return promise;
}

func()
	.then(function () {
		return func('hello');
	})
	.then(value => {
		return func(value + 'lagou');
	})
	.then(value => {
		return func(value + 'I ♥ U');
	})
	.then(value => {
		console.log(value);
	});
